dt-bindings: watchdog: renesas,wdt: Document r8a7742 support

RZ/G1H (R8A7742) watchdog implementation is compatible with R-Car Gen2,
therefore add relevant documentation.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1589555337-5498-17-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/renesas,wdt.txt

@@ -5,6 +5,7 @@ Required properties:
 		fallback compatible string when compatible with the generic
 		version.
 	       Examples with soctypes are:
+		 - "renesas,r8a7742-wdt" (RZ/G1H)
 		 - "renesas,r8a7743-wdt" (RZ/G1M)
 		 - "renesas,r8a7744-wdt" (RZ/G1N)
 		 - "renesas,r8a7745-wdt" (RZ/G1E)